Carisoprodol and Aspirin Tablets

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Carisoprodol and Aspirin Tablets contain NLT 90.0% and NMT 110.0% of the labeled amounts of carisoprodol (C₁₂H₂₄N₂O₄) and aspirin (C₉H₈O₄).

2 IDENTIFICATION

A. The retention times of aspirin and carisoprodol from the Sample solution correspond to those of Standard solution A, as obtained in the Assay.

3 ASSAY

Procedure

Buffer: Combine 5 mL of glacial acetic acid and 500 mL of water, and pass the mixture through a membrane filter of 0.5-μm or finer pore size.

Use the filtrate.

Mobile phase: Methanol and Buffer (64:36)

Diluent: Acetonitrile, glacial acetic acid, and water (40:1:59)

Standard solution A: USP Reference Standards in Diluent as listed below and prepared as follows. Transfer 80 mg of USP Aspirin RS and 80Jmg of USP Carisoprodol RS to a 25-mL volumetric flask. Add 15 mL of Diluent, swirl for 5 min, and sonicate for 25–30 s. Dilute with Diluent to volume.

Aspirin: 3.2 mg/mL of USP Aspirin RS

Carisoprodol: 3.2J mg/mL of USP Carisoprodol RS, where J is the ratio of the labeled amount, in mg, of carisoprodol to the labeled amount of aspirin

Standard solution B: 0.016 mg/mL of USP Salicylic Acid RS in Diluent

System suitability solution: 0.5 mg/mL of salicylic acid in Standard solution A

Sample solution: Nominally 3.25 mg/mL of aspirin prepared as follows. Finely powder NLT 20 Tablets. Transfer a portion of powder, equivalent to 325 mg of aspirin, to a 100-mL volumetric flask. Add 50 mL of Diluent, and swirl for 5 min. Sonicate for 25–30 s, shake by mechanical means for 30 min, and dilute with Diluent to volume. Pass a portion of this solution through a membrane filter of 0.5-μm or finer pore size, and use the filtrate within 8 h.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector

Aspirin and carisoprodol: Refractive index

Salicylic acid: UV 313 nm

Column: 4.6-mm × 25-cm; packing L7

Temperatures

Refractive index detector: 30 ± 1°

Column: 30 ± 1°

Flow rate: 1 mL/min

Injection volume: 50 μL

System suitability

Samples: Standard solution A, Standard solution B, and System suitability solution

[Note—The relative retention times for aspirin, salicylic acid, and carisoprodol are about 0.6, 0.7, and 1.0, respectively.]

Suitability requirements

Resolution: NLT 1.2 between solvent and aspirin; NLT 1.5 between aspirin and salicylic acid, System suitability solution using the refractive index detector

Relative standard deviation: NMT 2.0% for Standard solution A using the refractive index detector; NMT 5.0% for Standard solution B at 313 nm

Analysis

Samples: Standard solution A and Sample solution 

Calculate the percentages of the labeled amounts of aspirin (C₉H₈O₄) and carisoprodol (C₁₂H₂₄N₂O₄) in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) × 100

r_U = peak response of aspirin or carisoprodol from the Sample solution

r_S = peak response of aspirin or carisoprodol from Standard solution A

C_S = concentration of USP Aspirin RS or USP Carisoprodol RS in Standard solution A (mg/mL)

C_U = nominal concentration of aspirin or carisoprodol in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0% of the labeled amounts of carisoprodol (C₁₂H₂₄N₂O₄) and aspirin (C₉H₈O₄)

4 PERFORMANCE TESTS

Dissolution 〈711〉

Medium: Water; 900 mL

Apparatus 2: 75 rpm

Time: 45 min

Buffer: Glacial acetic acid in water (1 in 50)

Mobile phase: Methanol and Buffer (51:49)

Standard solution: USP Reference Standards as listed below and prepared as follows. Transfer 90 mg of USP Aspirin RS and 90J mg of USP

Carisoprodol RS to a 250-mL volumetric flask. Add 5 mL of acetonitrile, previously passed through a membrane filter of 0.5-μm or finer pore size, and swirl to dissolve. Dilute with water to volume.

Aspirin: 0.36 mg/mL of USP Aspirin RS

Carisoprodol: 0.36J mg/mL of USP Carisoprodol RS, where J is the ratio of the labeled amount, in mg, of carisoprodol to the labeled amount of aspirin

System suitability solution: 0.36 mg/mL of salicylic acid in the Standard solution

Sample solution: Filter a portion of the solution under test. Use the filtrate.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: Refractive index

Column: 3.9-mm × 30-cm; packing L1

Temperatures

Detector: 30 ± 1°

Column: 30 ± 1°

Flow rate: 2 mL/min

Injection volume: 300 μL

System suitability

Samples: Standard solution and System suitability solution

[Note—The relative retention times for aspirin and carisoprodol are 0.4 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 1.5 between aspirin and salicylic acid; NLT 1.5 between carisoprodol and salicylic acid, System suitability solution

Relative standard deviation: NMT 2.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amounts of aspirin (C₉H₈O₄) and carisoprodol (C₁₂H₂₄N₂O₄) dissolved:

Result = (r_U/r_S) x C_S × V × (1/L) × 100

r_U = peak response of aspirin or carisoprodol from the Sample solution

r_S = peak response of aspirin or carisoprodol from the Standard solution

C_S = concentration of USP Aspirin RS or USP Carisoprodol RS in the Standard solution (mg/mL)

V = volume of the Medium, 900 mL

L = label claim of aspirin or carisoprodol (mg/Tablet)

Tolerances: NLT 75% (Q) of the labeled amounts of aspirin (C₉H₈O₄) and carisoprodol (C₁₂H₂₄N₂O₄) are dissolved.

Uniformity of Dosage Units 〈905〉: Meet the requirements for Content Uniformity with respect to aspirin and to carisoprodol

5 IMPURITIES

Limit of Free Salicylic Acid

Mobile phase, Diluent, Standard solution B, System suitability solution, Sample solution, Chromatographic system, and System suitability: Proceed as directed in the Assay.

Analysis

Samples: Standard solution B and Sample solution

Calculate the percentage of free salicylic acid in the portion of Tablets taken:

Result = (r_U/r_S) x (C_S/C_U) × 100

r_U = peak response of salicylic acid from the Sample solution

r_S = peak response of salicylic acid from Standard solution B

C_S = concentration of USP Salicylic Acid RS in Standard solution B (mg/mL)

C_U = nominal concentration of aspirin in the Sample solution (mg/mL)

Acceptance criteria: NMT 3.0% of free salicylic acid

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Aspirin RS

USP Carisoprodol RS

USP Salicylic Acid RS